Synthesis And Characterization Of Thiophene Optoelectronic Materials With Quasi-Three Dimensional Structure

The organic molecular materials with quasi-three dimensional structure have been extensively researched in the organic light emitting diode, organic photovoltaic and organic effect transistor. The structure with two conjugated chains connected by one single bond was one of the typical representatives of quasi-three dimensional structure, presenting the shape of oblique cross-"X", which must weaken intermolecular?-? stacking to increase intrinsic solubility. By controlling the tortuosity of the backbone, we can get the desired solid state-crystalline state and amorphous state. In virtue of its binding method, the molecules were flexible and could adjust its spatial structure, conducive to form homogeneous film via spin-coating, according to van der Waals interaction force, ?-? stacking interaction of conjugate unit or other external force. Owing to the unique properties of quasi-three dimensional structure, a series molecules have been designed and synthesized with 3,3'-bithiophene and 2,2'-bithiophene as the central nodes, electron-donating and electron-withdrawing group as backbone, alkyl chain and ether chains as branch chain. By discussing the change of solid state from crystalline state to amorphous state, how to influence the UV absorption wavelength and hole mobility. On this basis, their application in organic solar cells as electron donors and in perovskite solar cells as hole transporting materials. The following are the main work in this thesis:1) Five A-D-A type moleculars-ST10-CN-1, ST10-CN-2, TM25, DDETM5T and DDETM5T3H with molecular weight about 1500-3000 g/mol were synthesized by Stille coupling, in which 3,3'-bithiophene as the central nodes, cyanacetate ethyle, thiophene imide and rhodanine derivatives as four arms. The molecular energy level was effected by the electron-withdrawing group and intramolecular charge-transfer. From the DSC testing results, I found that the change of terminal electron-withdrawing group has a great effect on crystallinity. Compared to the good crystallinity of ST10-CN-1 and ST10-CN-2, TM25 is bad, however DDETM5T and DDETM5T3H lost its crystallinity. By testing the hole mobility, the crystalline materials have better mobility than the amorphous materials. The five materials were used as electron donor materials and blended with the PCBM as electron acceptor to prepare the organic solar cells by solution processing. Because of the low short-circuit current, power conversion efficiency is very low. By analyzing the morphology, the films do not form good two phase separation structure between donor materials and acceptor materials, indicating exciton is recombined during transmission.2) Used 3,3'-bithiophene as the central nodes, three moleculars (DHPT-SC, DOPT-SC and DEPT-SC) were efficiently synthesized. According to the crystal structure, the two cross centre cores of DOPT-SC exhibit accurate 63.7° dihedral angle, showing the "X" swivel-cruciform structure. The coplanar thiophene rings were observed to overlap with another four counterparts of nearby molecules by offset-face-to-face pattern. Paralleled to other two adjacent planes, the shortest stacking distances with weak edge-edge overlap were evaluated to be 3.375 A. By testing the hole mobility, DEPT-SC based device has higher hole mobility than that of DHPT-SC and DOPT-SC, but three times less than F4TCNQ-doped DEPT-SC. Using DEPT-SC as dopant-free hole transport material, perovskite solar cells yields the best efficiency of 9.73%, compared 8.35% of DHPT-SC and 8.69% of DOPT-SC. It indicates that DEPT-SC device has the best charge collection efficiency. This could be contributed to the polar ether chain, which can easily form dipoalr interaction with the functional group CH3NH3+ of perovskite. The stronger van der waals force may be beneficial for the hole-extraction between the interfaces of DEPT-SC and perovskite. Futher, the CH3NH3PbI3-based perovskite solar cells using DEPT-SC doped with F4TCNQ as hole transport material exhibited a power conversion efficiency of 11.52%. Compared to the pristine devices, the perovskite solar cells using the new synthesized HTM showed an increased efficiency by about 18% and exhibited better photo-stability by the formation of molecular charge transfer complexes between F4TCNQ and DEPT-SC, indicating that the organic dopant is an effective method for DEPT-SC toward stable perovskite solar cells.3) Based on the molecular with 3,3'-bithiophene structure, four moleculars (BT-BHT, BT-BMeT, BT-BET and BT-OMeTAD) were efficiently synthesized and characterized by using more distorted 2,2'-bithiophene as the central nodes. The DSC testing results indicate that the four materials are all amorphous. Although losing the regularity of periodic molecular arrangement, these materials get better solubility, film-forming property and isotropy. From the UV-spectrum, the redshift phenomenon was observed, indicating the existence of ?-? stacking by intermolecular conjugate units. The hole mobility was tested by hole-only device. The mobility of amorphous BT-OMeT reachs up to 2.75* 10-4 cm2 V-1 s-1, which is biggest among all the molecular in this thesis. It can indicate that mobility is associated with the form of materials, but also closely connected with reaction between molecular conjugate chain. The CH3NH3PbI3-based perovskite solar cells using BT-BHT as dopant-free hole transport material exhibited a power conversion efficiency of 8.79%. Compared to that of isomeride DHPT-SC, BT-BHT has better solubility to get good film, resulting to higher fill factor and PCE. In the same condition, the device based on BT-BMeT exhibited slightly low PCE of 7.1%, but it is worth mentioning that the Jsc reached 17.3 mA cm"2.